Device and method for identifying defects during the feeding of a welding rod

ABSTRACT

The invention relates to a device for identifying defects during the feeding of a welding rod. A sensor assembly is located in the welding torch for detecting the feed pressure and the feed tension for the welding rod, a drive device for feeding the welding rod being located downstream of the sensor assembly in the feed direction of the welding rod (in the direction of the arrow).

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. §119 of Austrian ApplicationNo. A 660/2001 filed on Apr. 24, 2001. Applicant also claims priorityunder 35 U.S.C. §365 of PCT/AT02/00115 filed on Apr. 18, 2002. Theinternational application under PCT article 21(2) was not published inEnglish.

The invention relates to a device and a method for detecting errors inthe welding wire feed rate.

Patent specification JP-A-500-49137 describes a welding plant, in whichthe welding wire is fed along from a wire roller via a hose pack to awelding torch. The welding plant has two drive systems, the first drivesystem being disposed in the region of the wire roller, from which thewelding wire is fed into the hose pack. The second drive system isdisposed in the region of the welding torch and feeds the welding wirefrom the hose pack into the welding torch. The hose pack terminatesimmediately upstream of the second drive system as viewed in the feeddirection of the welding wire, as a result of which the wire corefollows a curved path in the form of a bend between the hose pack andthe drive system. Two contact elements co-operate with this bend so thata contact is established between one of the two contacts and the wirecore depending on the size of the bend. This system enables excesswelding wire between the two drive systems to be detected so that whenthe wire core comes into contact with one of the two contact elements, areduction or increase in the feed rate of at least one drive system isinitiated.

Patent specification U.S. Pat. No. 4,261,500 A also describes a wirefeed system for advancing a welding wire over a large distance on amodular basis. The wire feed system has several drive systems, inparticular a pushing module, an intermediate pushing module and apulling module. The pushing drive system co-operates with the wireroller whereas the pulling drive system co-operates with the weldingtorch. The intermediate pushing module is positioned between these two.Means are also provided between the pushing and pulling drive systemsfor detecting the welding wire feed rate.

A device is known from patent specification JP-A-49-42550, in which thewelding wire is fed between two rollers, which are spring-mounted via anarm. The arm is connected to a potentiometer so that a change inresistance occurs when the rollers move. The device is positionedbetween the two wire feeds. The first wire feed co-operates with thewire roller and feeds the welding wire from the wire roller via thedevice into the hose pack. The welding wire is also fed forward by thesecond wire feed, which is disposed in the welding torch or in theregion of the welding torch, in other words downstream of the hose pack.When a change in resistance occurs due to a roller movement, at leastone wire feed is regulated in order to synchronize the two wire feeds,thereby ensuring a constant feed rate.

Devices and a sensor system are already known from Austrian patentapplication No. A 1968/99, entitled “Welding wire feed system with mainand auxiliary drive”, filed by the present applicant. It describes asystem whereby the welding wire is deflected from its feed direction inorder to detect the feeding pressure. The sensor system or tubularsensor described in this application is used as a means of regulatingthe feeding pressure. This being the case, the device or tubular sensoris adapted accordingly so that it can be used to operate the solutionproposed by the invention.

The underlying objective of the invention is to propose a device and amethod of detecting errors in the welding wire feed rate, wherebydelivery of the welding wire and in particular the feeding pressureand/or the feeding traction can be monitored.

This objective is achieved due to the fact that a sensor system isprovided in the welding torch for detecting the feeding pressure andfeeding traction applied to the welding wire, the sensor system having adrive mechanism for the welding wire downstream of it in the directionin which the welding wire is fed.

The advantage of this approach is that providing the sensor systemenables burning to be detected or a defect in the pipe bend of thewelding wire as well as wear of the wire core or a fault on the wirefeed system upstream of the sensor system. This also means that it ispossible to ascertain whether a fault has occurred or is shortly aboutto occur upstream or downstream of the sensor system.

Other advantageous embodiments are described in claims 2 to 7. Theresultant advantages may be found in the description.

The objective is also achieved by the invention due to the fact that afeeding pressure and a feeding traction of the welding wire are detectedby a sensor system disposed in the welding torch and the sensor systememits a signal whenever the pressure is too high or too low, prompting acontrol system to run an evaluation.

The advantage of this is that providing the sensor enables caking of thewelding wire and wear of the wire core to be detected, so that thecontrol system of the welding wire is prompted to initiate measuresaccordingly.

Other advantageous features are described in claims 8 to 13. Theresultant advantages may be found in the description.

The invention will be described in more detail below with reference toan example of an embodiment.

Of the Drawings:

FIG. 1 is a schematic diagram of a welding machine or welding apparatus;

FIG. 2 is a simplified, schematic diagram showing an embodiment of adevice, in particular a sensor system, for the welding torch, whichdetects feeding pressure and feeding traction.

Firstly, it should be pointed out that the same parts described in thedifferent embodiments are denoted by the same reference numbers and thesame component names and the disclosures made throughout the descriptioncan be transposed in terms of meaning to same parts bearing the samereference numbers or same component names. Furthermore, the positionschosen for the purposes of the description, such as top, bottom, side,etc,. relate to the drawing specifically being described and can betransposed in terms of meaning to a new position when another positionis being described. Individual features or combinations of features fromthe different embodiments illustrated and described may be construed asindependent inventive solutions or solutions proposed by the inventionin their own right.

FIG. 1 illustrates a welding system and a welding apparatus 1 for awhole range of welding processes, e.g. MIG-MAG welding and TIG weldingor electrode welding processes.

Clearly, the solution proposed by the invention may be used with acurrent source or a welding current source.

The welding apparatus 1 has a welding current source 2 with a powercomponent 3, a control system 4 and a switching element 5 co-operatingwith the power component 3 and control system 4. The switching element 5or the control system 4 is connected to a control valve 6 incorporatedin a supply line 7 for a gas 8, in particular an inert gas such as CO₂,helium or argon and such like, running between a gas storage 9 and awelding torch 10.

Furthermore, a wire feed device 11 such as commonly used for MIG-MAGwelding may also be activated via the control system 4 in order to feeda welding wire 13 from a supply reel 14, preferably through a supplyline 12 or through a wire core, into the region of the welding torch 10.Clearly, the wire feed device 11 could also be integrated in the weldingapparatus 1, in particular in the basic housing, in a manner known fromthe prior art, rather than used as an add-on device as illustrated inFIG. 1.

The current needed to strike an arc 15 between the welding wire 13 and aworkpiece 16 is fed via a supply line 17 from the power component 3 ofthe current source 2 to the welding torch 10 and the welding wire 13,the workpiece 16 to be welded also being connected to the weldingapparatus 1, in particular to the current source 2, via another supplyline 18 so that an electric circuit can be established across the arc15.

In order to cool the welding torch 10, the welding torch 10 can beconnected via a cooling circuit 19, with an integrated flow indicator20, to a fluid container, in particular a water container 21, so thatthe cooling circuit 19, in particular a fluid pump used to pump theliquid contained in the water container 21, can be activated when thewelding torch 10 is switched on, thereby enabling the welding torch 10and the welding wire 13 to be cooled, for example via coolant lines.

The welding apparatus 1 also has an input and/or output device 22, bymeans of which a whole range of settings can be entered for weldingparameters and operating modes of the welding apparatus 1 or softwareprogrammes set up. The welding parameters entered at the input and/oroutput device 22 are then forwarded to the control system 4, from wherethey are applied to the individual components of the welding system andthe welding apparatus 1.

In the embodiment illustrated as an example here, the welding torch 10is also connected to the welding apparatus 1 and the welding system bymeans of a hose pack 23. The individual lines from the welding apparatus1 to the welding torch 10 are run through the hose pack 23. The hosepack 23 is connected by means of a connector device 24, known from theprior art, to the welding torch 10, whilst the individual lines in thehose pack 23 are connected to the individual contacts of the weldingapparatus 1 by means of connecting sockets and plug connectors. Torelieve tension on the hose pack 23, the hose pack 23 is connected via atension-relieving device 25 to a housing 26, in particular the basichousing of the welding apparatus 1.

FIG. 2 is a cut-away illustrating a detail of the welding torch 10,which is provided with a device for detecting faults in the welding wirefeed rate.

The device is provided in the form of a sensor system 27, disposed inthe welding torch 10. The sensor system 27 may be of various differenttypes and is not limited to the embodiment illustrated as an examplehere. The essential factor is that the sensor system 27 is disposed inthe welding torch 10 and is designed to detect the feeding pressure andfeeding traction applied to the welding wire 13. For example, the sensorsystem 27 may be provided in the form of a tubular sensor, of the typefor which Austrian patent application A 1968/99 was filed, entitled“Welding wire feed system with main and auxiliary drive”.

In the embodiment illustrated as an example here, the sensor system 27is provided in the form of a rotating wheel 28, which is rotatablymounted via a retaining element 29 so that the rotating wheel 28 sits incontact with the welding wire 13. As also illustrated, the sensor system27 also has a drive system 31 for feeding the welding wire, disposeddownstream of it in the direction in which the welding wire 13 isfed—indicated by arrow 30. The welding torch 10 used is of the typewhere the wire feed runs directly into the welding torch 10 and anotherdrive system—not illustrated—is therefore also provided in the weldingapparatus 1 or in a wire feed device 11.

The purpose of this drive system disposed in the welding apparatus 1 orin the wire feed device 11 is to force the welding wire 13 from thesupply reel 14 and simultaneously build up a feeding pressure to pushthe welding wire 13 through the hose pack 23. The other drive system 31in the welding torch 10, on the other hand, effects a pulling motion, inparticular a feeding traction, on the welding wire 13, i.e. the drivesystem 31 pulls the welding wire 13 out of the hose pack 23 and thenadvances it to the contact sleeve of the welding torch 10—notillustrated. With this system, it has been found to be of advantage ifthe drive system 31 is positioned very close to the contact sleeve ofthe welding torch 10.

However, to enable the feeding pressure and feeding traction to bedetected, the sensor system 27 or rotating wheel 28 must cause thewelding wire 13 to deflect out or deflect aside from its feed direction,i.e. the welding wire 13 in the welding torch 10 must be deflected sothat it assumes a curved path. This enables the feeding pressure andfeeding traction to be detected depending on the extent of the bend ordeflection because the extent of the bend or deflection in the weldingwire 13 varies depending on the feeding pressure and feeding traction.Consequently, if the bend or deflection is too small, the sensor system27 will emit a “feed pressure too low” signal, where as if the bend ordeflection is too high, the sensor system 27 will emit a “feed pressuretoo high signal”.

Different bends or deflections can be induced in the welding wire 13because the welding wire 13 is not actually fed through the sensorsystem 27, thereby making a deflection possible, i.e. a wire core 32 inwhich the welding wire 13 is run through the hose pack 23 to the weldingtorch 10 or a guide hose terminates short of the sensor system 23 orinside the sensor system 27, at which point the welding wire 13 runsfree. Naturally, it would also be possible for the welding wire 13 tothen be fed back into a wire core 32 or into a guide hose.

However, in order to be able to produce a deflection in a predefineddirection, the welding wire 13 must effect a predefined deflection,which is induced by the rotating wheel 28, whilst it is still in thesensor system 27. This being the case, if the feeding pressure is toohigh, the welding wire 13 will be deformed farther in the region of thesensor system 27, leading to an increase in the deflection or extent ofbending because more welding wire 13 is fed into the sensor system 27than is being pulled out by the drive mechanism 31. In the reversesituation, in other words when the feeding pressure is too low, thedrive mechanism 31 feeds more welding wire 13 out of the sensor system27 in the welding torch 13 than is delivered by the drive mechanism inthe welding apparatus 1 or the wire feed device 11, so that thedeflection or extent of bending is lessened.

This motion of the welding wire 13 can therefore be used as a basis fordetermining whether the feeding pressure or feeding traction is actingon the welding wire 13 as it is fed along, enabling the feeding pressureand feeding traction to be detected, prompting corresponding signals orprocess steps to be initiated or ceased. This being the case, thecontact force of the rotating wheel 28 on the welding wire 13 can beadjusted via an adjusting mechanism 33, specifically to deflect thewelding wire 13, i.e. the adjusting mechanism 33 can set the deflectionand hence the feeding pressure, because the rotating wheel 28 and hencethe welding wire 13 are deflected at an appropriate pressure by theadjusting mechanism 33, so that this pressure must first be overcome inorder to displace the rotating wheel 28.

When the welding wire 13 is deflected transversely to its feed directiondue to a pressing force applied via the deflector roller or via therotating wheel 28, the deflection of the welding wire 13 will remainunchanged if the pushing and pulling action on the welding wire 13 isequal. In other words, the quantity of welding wire 13 pushed forwardscorresponds to the quantity of welding wire 13 pulled along by the drivemechanism 31 and the welding wire 13 is “tension-free”, i.e. it istension-free and pressure-free in its longitudinal direction in thecross-sectional region of the rotating wheel 28, in other wordssubjected to neither a pressure force or a traction force. If, on theother hand, the quantity of welding wire being pulled along is sloweddown by the drive mechanism 31, more welding wire 13 is being deliveredand this leads to an increase in pressure in the welding wire 13 in thecross-section of the contact region of the rotating wheel 28 and to amore pronounced deflection of the welding wire 13.

If, on the other hand, more welding wire 13 is being pulled away fromthe region of the rotating wheel 28 than is being delivered by a feedmechanism, not illustrated of the device proposed by the invention fordetecting faults in the welding wire 13, which is positioned upstream byreference to the feed direction, a traction force will be generated inthe welding wire 13 in the region of the rotating wheel 28, which causesthe welding wire 13 to change position opposing the deflection force ofthe rotating wheel 28 of the sensor system 27, and hence the rotatingwheel 28, against the pressing force generated via the rotating wheel28. Consequently, not only is the device proposed by the invention ableto detect the pressure build-up in the welding wire 13 when the quantityof welding wire 13 conveyed down-stream is too high, it is also able todetect the build-up of too high a traction force caused by the drivemechanism 31 in the welding torch 10. Naturally, the build-up of toohigh a traction force in the welding wire 13 can also be output as asignal or an indication can be issued to the effect that the detectedfeed pressure is too low. Accordingly, this system for the first timeprovides a means of determining when there is an increase above or dropbelow a certain feeding pressure and/or feeding traction and does so ina surprisingly simple manner.

In the embodiment illustrated as an example here, the adjustingmechanism 33 is designed so that a positioning element 34 with aco-operating spring 35 causes a build-up of pressure force on therotating wheel 28. However, an appropriate pressure is generated in onedirection only, although the adjusting mechanism 33 may naturally bedesigned so that it can generate an appropriate pressure in bothdirections of the pivoting motion of the rotating wheel 28.

The rotating wheel 28 and/or the retaining element 29 is also connectedto a contact element 36 to enable the deflection of the rotating wheel28 and hence the deflection of the welding wire 13 to be detected viathe contact element 36. In the embodiment illustrated as an examplehere, the contact element 36 is provided in the form of two contacts 37,38, between which a contact strip 39 is disposed. The contact strip 39is also joined to the rotating wheel 28 and the retaining element 29 sothat when the rotating wheel 28 is deflected far enough, the contactstrip 39 sits against one of the two contacts 37, 38, thereby emittingan electric signal. When the deflection is increased, the extent ofbending increases so that the contact strip 39 is moved into abutmentwith the contact 38, whereas when the deflection if reduced, the contactstrip 39 is moved into contact with the oppositely lying contact 37.

An exact description of how a sensor system 27 of this type works willnot be given in detail because the operating principle is very simple.It should be merely be pointed out that the welding wire 13 is fed inthe direction indicated by arrow 30 and the welding wire 13 isdeliberately deflected by the rotating wheel 28, so that the pivotingmotion of the rotating wheel 28, in particular the deflecting motion, isdetected.

By fitting the welding 10 torch with a sensor system 27 of this type, itis now possible to run a process for detecting faults in the weldingwire feed rate. The sensor system 27 in the welding torch 10 detects thefeeding pressure and feeding traction of the welding wire 13 and asignal is emitted by the sensor system 27 whenever the feeding pressureand feeding traction is too high or too low. The signals output by thesensor system 27 may then be further processed by a control system, inparticular by the control system 4 of the welding apparatus 1 andspecific measures initiated on the basis of these signals. Accordingly,on the basis of an evaluation by the control system 4 of the weldingapparatus 1, the signals from the sensor system 27 may be correlatedwith the welding process so that during welding start-up, for example,the control system 4 can ascertain that any “feed pressure too low”signal which occurs is not attributable to a fault because the feedingpressure has yet to be built up at this stage. This signal can thereforebe suppressed by the control system 4. Correlating the signals from thesensor system 27 with the states of the welding process therefore offersconsiderable advantages because the control system 4 is able toascertain whether there actually is a fault or whether the signal wasgenerated due to a change in the welding process.

When the “feed pressure too high” signal is emitted, in other words whenthe contact strip 39 comes into contact with the contact 38, the controlsystem 4 is informed that a fault is shortly about to occur in thewelding wire feed system downstream of the sensor system 27, inparticular burning and caking of the welding wire 13 on the contactsleeve, enabling the control system 4 to initiate whatever precautionsare needed to prevent burning. If, on the other hand, the “feed pressuretoo low” signal is emitted, in other words the contact strip 39 has comeinto contact with the contact 37, the control system 4 is informed thata fault is about to occur in the welding wire feed system at a pointbefore the sensor system 27, in particular wear of the wire core. Thecontrol system is therefore able to output a warning signal, forexample, so that the wire core 32 can be replaced at the nextopportunity.

It is therefore now possible, for the first time, to detect caking andburning of the welding wire 13 on the contact sleeve before it happensand initiate appropriate regulation and control procedures, which hassignificant advantages, especially in automatic welding plants. Thewelding wire 13 can be detected upstream of the sensor system 27 becauseshortly before the welding wire 13 burns and cakes on the contactsleeve, the drive mechanism 31 in the welding torch 10 reduces the feedrate of the welding wire 13 due to the increase in friction losses,causing an increase in the extent of bending or deflection, which isdetected by the sensor system 27. Consequently, the control system 4 canbriefly reduce the welding current, for example, which in most caseswill prevent the welding wire 13 from burning and caking.

Wear on the wire core 32 can be detected because when the feedingpressure is constant, friction losses in the wire core 32 are increased,which means that not so much wire 13 can be delivered by the drivemechanism in the welding apparatus 1 or in the wire feed device 11 andmore welding wire 13 is therefore pulled along by the drive mechanism 31in the welding torch 10, thereby reducing the extent of bending ordeflection in the welding wire 13 in the sensor system 27.

Detecting burning of the welding wire 13 and wear on the wire core 32prevents premature downtimes in automatic welding plants due to faultsin the welding wire feed system, thereby reducing down-time costs.

Naturally, the contact element 36 could also be designed so that themotion of the rotating wheel 28 is monitored on a constant basis. Tothis end, the rotating wheel 28 may be connected to a potentiometer oran incremental transmitter, for example, so that a signal can be emittedwhen pre-set desired values are exceeded or the values may be evaluateddirectly by the control system 4.

For the sake of good order, it should be pointed out that in order toprovide a clearer understanding of the design of the welding apparatus 1and the sensor system 27, they and their constituent parts areillustrated to a certain extent out of proportion and/or on an enlargedscale and/or on a reduced scale.

The independent solutions proposed by the invention and the underlyingobjectives may be found in the description.

Above all, the individual embodiments of the invention illustrated inFIGS. 1; 2 may be construed as independent solutions proposed by theinvention in their own right. The associated objectives and solutionsmay be found in the detailed descriptions of these drawings.

List of reference numbers 1 Welding apparatus 2 Welding current source 3Power component 4 Control system 5 Switching element 6 Control valve 7Supply line 8 Gas 9 Gas storage 10 Welding torch 11 Wire feed device 12Supply line 13 Welding wire 14 Supply reel 15 Arc 16 Workpiece 17Welding line 18 Welding line 19 Cooling circuit 20 Flow indicator 21Water container 22 Input and/or output device 23 Hose pack 24 Connectingdevice 25 Tension-relieving device 26 Housing 27 Sensor system 28Rotating wheel 29 Retaining element 30 Arrow 31 Drive mechanism 32 Wirecore 33 Adjusting mechanism 34 Positioning element 35 Spring 36 Contactelement 37 Contact 38 Contact 39 Contact strip

1. System for detecting faults in the welding wire feed rate which maybe integrated in or mounted on a welding torch, in which a drive systemis disposed on or integrated in a welding torch and in a weldingapparatus, characterised in that the welding torch has a sensor system(27) for detecting the feeding pressure and/or feeding traction for thewelding wire (13), which is disposed in the welding torch (10) and thesensor system (27) has a drive mechanism (31) downstream of it in thefeed direction of the welding wire (13), and the sensor system (27)causes the welding wire to deflect out or deflect aside from its feeddirection in the welding torch (10).
 2. System as claimed in claim 1,characterised in that the sensor system (27) is provided in the form ofa rotating wheel (28), which is pivotably mounted via a retainingelement (29) and is designed to sit in contact with the welding wire(13).
 3. System as claimed in claim 2, characterised in that anadjusting mechanism (33) is provided to generate the contact force ofthe rotating wheel (28) on the welding wire (13), in particular togenerate the deflection.
 4. System as claimed in claim 2, characterisedin that the rotating wheel (28) and/or the retaining element (29) isconnected to a contact element (36).
 5. System as claimed in claim 4,characterised in that the contact element (36) is provided in the formof contacts (37, 38) and a contact strip (39).
 6. System as claimed inclaim 1, characterised in that the sensor system (27) is a tubularsensor.
 7. System as claimed in claim 1, characterised in that thesensor system (27) is designed to emit a “feed pressure too low” signalwhen the extent of bending or deflection in the welding wire (13) is toolow and to emit a “feed pressure too high” signal when the extent ofbending or deflection is too high.
 8. Method of detecting faults in thewelding wire feed rate, whereby the welding wire is fed from the wiresupply or wire roller via a drive system into a hose pack and from thereis fed via another drive system in the welding torch or in the region ofthe welding torch on to the welding point, characterised in that afeeding pressure and a feeding traction of the welding wire are detectedby a sensor system in the welding torch and the sensor system emits asignal whenever the feeding pressure is too high or too low, and thesensor system has a drive system in the welding torch disposeddownstream of it in the feed direction of the welding wire, which causesthe welding wire (13) to deflect out or deflect aside from its feeddirection in the welding torch (10).
 9. Method as claimed in claim 8,characterised in that the welding wire is deflected by the sensorsystem.
 10. Method as claimed in claim 8, characterised in that thesensor system has a rotating wheel, and the motion of the rotatingwheel, in particular the deflecting motion, is detected.
 11. Method asclaimed in claim 8, characterised in that the “feed pressure too high”signal informs a control system that a fault is shortly about to occurdownstream of the sensor system, in particular burning of the weldingwire on the contact sleeve.
 12. Method as claimed in claim 8,characterised in that the “feed pressure too low” signal informs acontrol system that a fault is shortly about to occur upstream of thesensor system, in particular wear on the wire core.
 13. Method asclaimed in claim 8, characterised in that the signals of the sensorsystem are further processed by a control system.